This invention relates to electroluminescent (EL) lamps and, in particular, to an EL lamp providing illumination in two, parallel planes.
An EL lamp is essentially a capacitor having a dielectric layer between two conductive electrodes, one of which is transparent. The dielectric layer, or a separate layer, includes a phosphor powder which radiates light in the presence of a strong electric field, using very little current. The front electrode is typically a thin, transparent layer of indium tin oxide or indium oxide and the rear electrode is typically a polymer binder, e.g. polyvinylidene fluoride (PVDF), polyester, vinyl, or epoxy, containing conductive particles such as silver or carbon. The front electrode is applied to a polymer substrate, such as polyester or polycarbonate, that provides mechanical integrity and support for the other layers.
Because of the uniformity of the light and the variety of colors of EL lamps, the number of applications for EL lamps grows steadily. EL lamps are planar or sheet devices and there are some applications in which a display is made in two or more stacked planes, as in watches having both an analog display and a digital display. The analog display is a dial and the digital display is a liquid crystal display (LCD) located within the dial. A single EL lamp cannot be used to backlight both displays because an LCD is much thicker than a dial face. Space in a watch is conserved by cutting a hole or window in the dial and positioning the LCD in the window. Even so, the thickness of an LCD precludes the use of a single EL lamp for backlighting both displays. Thus, two lamps and four electrical connections must be included in each analog/digital watch. Each connection adds cost and adds a small but finite chance for failure.
As used herein, an EL "panel" is a single substrate including one or more luminous areas, wherein each luminous area is an EL "lamp."
In view of the foregoing, it is therefore an object of the invention to provide a single EL panel having at least two lamps that can be stacked to provide lamps in at least two planes.
A further object of the invention is to provide a single EL panel having lamps in at least two parallel planes mechanically joined by a common substrate.
Another object of the invention is to provide a single EL panel having at least two lamps in different planes emitting light in substantially the same direction.
A further object of the invention is to provide a single EL panel having lamps in at least two parallel planes electrically interconnected by a single pair of conductors.